Ignoring any legal issues, "was Cesar ethically obligated to inform his partner, George, of his criminal past?"

The study of the Theory of Fundamental Rights is of paramount importance for the construction of the present work, because in addition to being the basis of the legal system of a State, the rules of fundamental rights occupy a prominent position in most constitutions.

The person has a right to privacy, so he has no obligation to tell about his past, he has a right to want to or not to tell it, it's up to him to decide.